Builds the url query parameters from an object

toUrlParams.js

const isObject = (it) => it != null && typeof it === 'object';

/**
 * Encodes an object to be used as query-string.
 * It uses 'encodeURIComponent' to set each value.
 *
 * @param {object} data an object with key-value pairs to create the query-string
 * @returns {string} the query-string
 */
function toUrlParams(data) {
  let value;
  if (!data) return '';
  const serialized = [];
  Object.keys(data).forEach((key) => {
    value = data[key];
    if (value === undefined) return; // continue;
    if (typeof value === 'function') return;
    if (isObject(value)) value = JSON.stringify(value);
    // key and value should be decoded with decodeURIComponent
    serialized.push(`${encodeURIComponent(key)}=${encodeURIComponent(value)}`);
  });
  return `?${serialized.join('&')}`;
}

usage.js

var data = {
  SRC: 10,
  gclid: "Cj0KEQjwnsPGBRDo4c6RqK",
  subid: 102,
  utm_medium: "cpc",
  utm_source: "google",
  utm_term: "market place",
};

var query = toUrlParams(data);
// expected:
// "?SRC=10&gclid=Cj0KEQjwnsPGBRDo4c6RqK&subid=102&utm_medium=cpc&utm_source=google&utm_term=market%20place"

/*
 * If you want to pass an array, or an object to the url,
 * they will be serialized as JSON and encoded with
 * encodeURIComponent.
 */
data = {
  id: 6716,
  data: {
    category: 'laptop',
    brands: ['DELL', 'ASUS'],
  },
};

query = toUrlParams(data);
// expected:
// "?id=6716&data=%7B%22category%22%3A%22laptop%22%2C%22brands%22%3A%5B%22DELL%22%2C%22ASUS%22%5D%7D"

/*
 * Tip: You may use the function urlParamsToObject
 * in order to convert the url parameters to an object.
 * See: https://gist.github.com/jherax/e6ecb05aa35eb0219525
 */